Blender video output settings change after render
Yes, if you most the time use to write out a certain format instead of the "currently" set default format.

Solution would be to make your setup default.


I'd suggest to go from a new file aka press Ctrl+N and make a new General scene.
Go in the Output Properties and set it up how you want it to be default.
Go in the File Menu->Defaults->Save Startup File



From now on, til you chose to "Load Factory Settings" you will have the new settings as default. This can be used for pretty much all settings, that's why it's best to go from a new clean scene, as to not accidentally set unwanted things as default.